Analysis of Air Quality Evolution in the Basque Autonomous Community Using Radial Basis Function Interpolation and Unsupervised Learning

Abstract

This study presents results from a spatial modeling and analysis process of six different air pollutants measured over a ten-year period at up to forty-three monitoring stations located in the three provinces of the Basque Autonomous Community (BAC) (Spain). The main objective was to generate detailed maps showing the evolution of these pollutants that cover the entire area using geostatistical techniques. These maps are intended to serve as a basis for both short-term and medium-term environmental studies, while also examining how pollutant levels have changed before and after the COVID-19 pandemic era. Additionally, the paper explores the factors that may explain the differences observed during these two periods. To further analyze the spatial patterns, the study employs the Fuzzy C-Means clustering algorithm to partition the region into four distinct zones based on the concentrations of key pollutants: PM₁₀, NO₂, and O₃. These pollutants were selected due to their high sampling density, spatial coverage, and complementary sources (traffic emissions, combustion processes, and ozone photochemistry), making them representative indicators of the region’s atmospheric state. The findings reveal significant changes in air quality during the COVID-19 pandemic, particularly in NO₂, Benzene, and CO levels, which sharply declined due to reduced vehicular traffic. However, the behavior of PM₁₀ and O₃ was more complex, influenced by diverse sources and atmospheric chemistry. The reduction in NO₂ emissions during lockdowns led to a counterintuitive increase in O₃ concentrations in some areas, highlighting the non-linear responses of atmospheric systems to emission changes. This study underscores the importance of multi-faceted air quality management strategies that account for the intricate interplay of different emission sources and atmospheric processes. The insights gained from this unique period should inform the development of more effective, evidence-based air quality policies for a healthier and more sustainable future.